On-chain Volume vs Volume on Exchanges
On-chain volume includes OTC. OTC (over-the-counter) purchases always clears onto the chain. Exchange volume does not. You can look at the volume going through the blockchain as an investment volume.
But the biggest problem with volume on exchanges is that we can’t reliably look at it since it’s faked. But you can't really fake onchain data, very difficult indeed.
Since almost no one is using on-chain metrics for trading purposes, there is no need to fake on-chain volume, and it's a lot more difficult: it's a lot of work and a lot more money is needed to do that.